The present invention relates to an electrophotography photosensitive body (henceforth, may be referred to as xe2x80x9cphotosensitive bodyxe2x80x9d) that can prevent contamination from a developing roller used in a printer having a non-magnetic single component developing system. Described in more detail, the present invention relates to an electrophotography photosensitive body concerned with improving the construction material of a charge transport layer that has organic material as the main component.
Electrophotography photosensitive bodies have a basic construction in which a photosensitive layer having a photoconductive function is layered on top of a conductive substrate. In recent years, there has been advances in research and development of organic electrophotosensitive bodies that use organic compounds as the functional component responsible for charge generation and transport. These have the advantages of having a variety of materials, high productivity and safety, and the like. Their applications for use in copiers and printers and the like have been advanced.
Currently, in printers, particularly low-speed printers, an inexpensive non-magnetic single-component developing system is used. They are manufactured for personal users or for office users. Furthermore, currently in the low speed printer market, although a monochrome system is still mainstream, demand for color printers using a non-magnetic single component developing system is growing. In the future, it is predicted that color printers will become mainstream.
Referring to FIG. 2, in non-magnetic single component developing systems, the outermost surface of the organic photosensitive layer of a photosensitive drum 6 and the outermost layer of a developing roller of a metal iron core 8 and a dielectric rubber material 7 are in contact. Toner 9, which is charged by the friction between toner 9 and the developing roller surface, adheres electrostatically to the developing roller surface. Toner 9 is made into a uniform thin layer by a metal blade 11. Toner 9 then has a bias voltage applied when it enters between photosensitive drum 6 and the developing roller. Toner 9 electrostatically adheres to the organic photosensitive body surface and is developed. Referring to the figure, there is also shown a printing paper 10.
The following are required qualities for the developing roller dielectric rubber used in the above non-magnetic single component developing system.
1) In order to have a suitable nip width, it must have a low hardness.
2) There is no permanent deformation with the deformation of the developing roller associated with contact.
3) In order to have the desired developing qualities, it should be in the semiconductor range of 105-1010 ohm cm.
For the properties of the developing roller surface and the area near the surface,
1) The desired charging polarity and charging amount is obtained by the friction generated with the toner.
2) Mold release with the toner is good, and there is no toner filming on top of the developing roller surface during use.
3) In order to have a uniform toner layer on top of the developing roller surface, the surface has a suitable surface roughness.
4) It has good abrasion resistance and has excellent durability.
5) With respect to the photosensitive body, there is no migration of components from the developing roller.
In order to have the desired developing roller quality, in addition to the rubber material, carbon black or white carbon (SiO2) and the like can be added as electrical resistance adjusting materials in order to give the desired electrical qualities. In addition, plasticizer or hardening agents and the like can be added to adjust the rubber hardness. Various other materials such as vulcanizing agents, vulcanization accelerator agents and the like can be added.
As described above, by adding various additives other than rubber materials, the desired electrical resistance, mechanical properties, and surface properties for the developing roller can be achieved. However, with regard to the problem of component migration from developing roller to the photosensitive body surface as described in 5) of the developing roller surface properties, this is not just a problem with the developing roller surface but it is also a problem with the roller interior. While the photosensitive body and the developing roller are in contact, under the right conditions of temperature and humidity, particularly under a high temperature/high humidity environment, the components from the developing roller migrate, and these components adhere to the photosensitive body surface. When printing is conducted by a photosensitive body having these adhering components, the printed text can be deformed, or there can be image deterioration such as voids generated in black and halftone images.
The object of the present invention is to solve the above problems and to prevent the contamination of the photosensitive body surface resulting from component migration from the developing roller. A further object is to provide an organic electrophotography photosensitive body that can achieve a stable image quality.
Intense study was conducted to solve the above problems. As a result, it was discovered the reason that the components from developing roller adhere to the photosensitive body surface (henceforth referred to as xe2x80x9cvolatile componentsxe2x80x9d) is because the high surface energy of the photosensitive body surface causes physical adhesion to occur.
In other words, the present invention is an electrophotography photosensitive body, being a function separated laminated electrophotography photosensitive body equipped with at least a charge generating layer and a charge transport layer on top of a conductive substrate and being used by mounting onto a printer of a non-magnetic single component developing system, wherein: a contact angle theta of pure water on the charge transport layer satisfies theta greater than =94 degrees.
In the present invention, the charge transport layer preferably contains a resin binder of only a polydialkyl siloxane-containing polycarbonate having a repeating unit represented by a following general formula (1) 
wherein each R is independently a C1-C6 alkyl group or an optionally substituted C6-C12 aromatic hydrocarbon group; B is (CH2)x; is an integer from 2-6; n is from 0-200; m from 1-50. Optionally, the charge transport layer can contain the polydialkyl siloxane-containing polycarbonate and another polycarbonate such that, with a weight M of the polydialkyl siloxane-containing polycarbonate and a weight N of the other polycarbonate is a ratio MIN which is greater than 1/4.
Even more preferably, the polydialkyl siloxane-containing polycarbonate has a repeating unit represented by a following formula (2), 
wherein, for x, y and z, the ratio of x/(x+y+z) is 0.5-0.95, and the ratio of z/(x+y+z) is 0.0001-0.1; n=0-200.
The above, and other objects, features, and advantages of the present invention will become apparent from the following description read in conjunction with the accompanying drawings, in which like reference numerals designate the same elements.